The present invention relates to a method for manufacturing a semiconductor device and the semiconductor device manufactured by the method, in which the semiconductor device is manufactured by laser cutting a plate having a number of such semiconductor devices.
Typically, a microwave high power device such as GaAs high power FET, including a semiconductor element, includes a thinned semiconductor substrate having a small thickness of about 30 xcexcm for an effective radiation of heat generated at a semiconductor element. Also, for further heat radiation, a radiation metal layer (PHS layer) is provided on one surface of the semiconductor substrate away from the semiconductor element.
PCT/WO98/13862 discloses a method for manufacturing a GaAs high power semiconductor device having such heat radiation metal layer, which is illustrated in FIGS. 5A to 5L. According to the method, as shown in FIG. 5A, a first main surface of GaAs substrate 31 carrying semiconductor elements is etched to form a first separation groove 33, in which a photoresist layer 32 provided on the first main surface is used as a mask. Then, as shown in FIG. 5B, the first separation groove 33 is plated with a first metal layer 34. As shown in FIG. 5C, the GaAs substrate 31 then has wax 35 applied on the first main surface and is further bonded onto a supporting wafer 36 made of glass or sapphire. Also, the GaAs substrate 31 is polished at its second main surface to reduce its thickness to about 20 to 30 xcexcm. Subsequently, as shown in FIG. 5D, the GaAs substrate 31 is provided at its second main surface with a photoresist layer 44 which is then patterned with an aperture opposing the first separation groove 33. The photoresist layer 44 so patterned is used as a mask for an etching in which the second main surface of the GaAs substrate 31 is etched to the extent that the bottom surface of the first metal layer 34 in the first separation groove 33 is exposed, which results in a second separation groove 63 shown in FIG. 5E.
Next, as shown in FIG. 5F, the photoresist layer 44 is removed and then a conducting layer 37 is plated on the entire second main surface of the GaAs substrate 31. Further, as shown in FIG. 5G, a photoresist 45 is provided on the conducting layer 37 which is used for a mask in the subsequent plating of a second metal layer 46 made of the same metal as that of the first metal layer 34. Afterwards, as shown in FIG. 5H, a photoresist layer 47 having a width smaller than that of the second separation groove 63 is formed in the second separation groove 63. With the photoresist layer 47 as a mask, a PHS layer 38 is formed on the second main surface of the GaAs substrate 31 by the 5 electroplating. Next, as shown in FIG. 5I, the GaAs substrate 31 is removed from the supporting wafer 36. In addition, as shown in FIG. 5J, an expandable film 40 is attached on the PHS layer 38. Then, the first and second metal layers, 34 and 46, are grooved and then separated from the first separation groove 33 by exposure to laser light, such as YAG laser light, as illustrated by the dotted line. This results in a semiconductor device shown in FIG. 5K. Finally, as shown in FIG. 5L, the semiconductor device is bonded at its bottom with a package 39 and is provided at its top with bonding wires 40 by a wirebonding technique, and then sealed in a ceramic package or a metal package not shown.
Generally, in the semiconductor device so manufactured, the topmost of the first metal layer 34 extends to a level of the first main surface of the GaAs substrate 31. Disadvantageously, the topmost of the first metal layer 34 can extend above the first main surface of the GaAs substrate 31 because the first metal layer is formed by the plating as described above. This may cause the bonding wire 40 to make an unwanted short-circuit with the first metal layer 34, which results in a reduction of yield rate of the device.
Therefore, an object of the present invention is to provide a method of manufacturing a semiconductor device in which no short-circuit would occur between the bonding wires and the first metal layer. Another object of the present invention is to provide a semiconductor device manufacture by the method.
Hence, the inventors of the present invention have intensively studied. As a result, the present inventors have found that the first metal layer is selectively formed in the first separation groove by an electroless plating technique using catalyst layer formed on the bottom of the first separation groove as a catalyst, so that the topmost of the first metal layer is located below that of the opening of the first separation groove, which ensures that no short circuit would occur between the bonding wire and the first metal layer, thereby accomplishing the present invention.
The present invention provides a method for manufacturing a semiconductor device, including the steps of: providing a substrate having first and second main surfaces and having a semiconductor element formed in the first main substrate; forming a first groove in the first main surface of the substrate, the first groove having a bottom surface with a width and opposing side surfaces on the bottom surface; forming selectively a catalyst layer on the bottom surface of the first groove, the catalyst layer containing palladium in an upper surface thereof; forming a fist metal layer of a nickel based plating layer on the upper surface of the catalyst layer by an electroless plating technique, a top portion of the first metal layer located at a distance below a top end of the side surface of the first groove; forming a second groove in the second main surface of the substrate along the first groove, the second groove having a bottom with a smaller width than that of the bottom of the first groove and opposing side surfaces on the bottom surface, the bottom surface of the second groove being a backside surface of the catalyst layer; forming a second metal layer overlying the bottom and side surfaces of the second groove; and laser-cutting the first metal layer, the catalyst layer, and the second metal layer through the first groove.
By using such a method, the first metal layer can be formed selectively in the first separation groove so that the topmost of the first metal layer is locate below that of the opening of the first separation groove, which ensures that no short circuit would occur between the bonding wire and the first metal layer.
Also, the catalyst layer containing palladium (Pd) is formed by a dry-processing technique, thereby deposition of palladium ion on outside of the first separation groove and forming nickel based plating layer on the portion where the palladium ion is deposited can be prevented.
Also, a deposit formed by reacting palladium ion and oxygen or the like can be prevented from forming on the bottom of the first separation groove.
After the step of forming the first metal layer, the method may further comprise the step of attaching a supporting member on the first main surface, and thinning the substrate through the second main surface.
Preferably, the step of forming the catalyst layer containing the steps of: forming a first photoresist layer on the first surface of the substrate, the photoresist layer having an opening opposing to the first groove; depositing a catalyst material on the bottom surface of the first groove through the first photoresist layer as a mask by evaporation or sputtering deposition; and removing the first photoresist layer together with the catalyst material on the photoresist layer, and remaining the catalyst material on the bottom surface of the first groove.
By using this step, the catalyst layer is formed selectively only on the bottom of the first separation groove.
By forming the nickel based plating layer using the palladium in the catalyst layer as a catalyst, the nickel based plating layer can be selectively formed only near the catalyst layer.
The catalyst layer preferably has two-layers of a palladium layer and a titanium layer under the palladium layer, or a single palladium layer.
The nickel based plating layer is preferably made of one material selected from Nixe2x80x94P alloy, Nixe2x80x94B alloy, and Nixe2x80x94Bxe2x80x94W alloy.
The present invention provides a semiconductor device, comprising: a semiconductor substrate having first and second main surfaces, having a semiconductor element formed in the first main surface and having a peripheral surface containing the first and second main surface; a heat radiation layer provided on the second main surface of the semiconductor substrate; and a flange of a plurality of metal layers disposed on the peripheral surface of the substrate, the metal layers comprising; a first metal layer having a surface layer containing palladium on the same side with the first main surface, a second metal layer of nickel based alloy disposed on the surface layer containing palladium of the first metal layer, and the second metal layer having a top portion located at a distance below the first main surface, and a third metal layer disposed under the first metal layer.
The metal layer provided on the peripheral surface of the substrate is formed away from the front surface of the semiconductor substrate, thereby the short circuit between the bonding wire and the metal layer can be prevented at the wirebonding of the semiconductor substrate.
The third metal layer may comprise a nickel based alloy layer, a gold layer and a laser-cut metal layer including a nickel layer or a chromium layer.
The third metal layer may further comprise a single layer of gold or a plurality of layers including a titanium layer and a gold layer on the laser-cut metal layer.
The wettability of the lower surface of the PHS layer against an AuSn solder used for bonding the lower surface of the PHS layer onto the package is improved.
The first metal layer preferably comprise two-layers of a palladium layer and a titanium layer under the palladium layer, or a single layer.
The second metal layer is preferably made of one material selected from Nixe2x80x94P alloy, Nixe2x80x94B alloy, and Nixe2x80x94Bxe2x80x94W alloy.
As will be clear from the above description, in the semiconductor device manufactured by the method of the present invention, the topmost of the first metal layer is located below the upper surface of the GaAs substrate, therefore the short circuit between the bondingwire and the first metal layer can be prevented, and the production yield of the semiconductor device can be increased.
Also, according to the method of the present invention, the catalyst layer including palladium is formed by dry-processing, therefore a deposit is not formed on the bottom of the first separation groove. Thereby the unevenness of the laser-cut layer, which makes defects in the laser cutting, is prevented and the yield of the semiconductor device can be increased.
Also, the nickel based plating layer is formed by using the catalyst layer as a catalyst, thereby the nickel based plating layer is prevented from forming on the outside of the first separation groove and the production yield can be increased.